1. Field of the Invention
The present invention relates primarily to the papermaking arts. Specifically, the present invention relates to seaming multi-layer integrally woven fabrics for use on papermaking machines.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
The present invention relates primarily to the fabrics used in the press section, generally known as press fabrics, but it may also find application in the fabrics used in the forming and dryer sections, as well as in those used as bases for polymer-coated paper industry process belts, such as, for example, long nip press belts, industrial fabrics and/or engineered fabrics such as pulp forming fabrics, sludge dewatering fabrics and Double Nip Thickener (DNT) dewatering fabrics, among others.
Press fabrics play a critical role during the paper manufacturing process. One of their functions, as implied above, is to support and to carry the paper product being manufactured through the press nip.
Press fabrics also participate in the finishing of the surface of the paper sheet. That is, press fabrics are designed to have smooth surfaces and uniformly resilient structures, so that, in the course of passing through the press nips, a smooth, mark-free surface is imparted to the paper.
Perhaps most importantly, the press fabrics accept the large quantities of water extracted from the wet paper in the press nip. In order to fulfill this function, there literally must be space, commonly referred to as void volume, within the press fabric for the water to go, and the fabric must have adequate permeability to water for its entire useful life. Finally, press fabrics must be able to prevent the water accepted from the wet paper from returning to and rewetting the paper upon exit from the press nip.
Contemporary press fabrics are used in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven base fabric into which has been needled a batt of fine, non-woven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of several synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric, produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the woven base fabrics may be laminated by placing one base fabric within the endless loop formed by another and by needling a staple fiber batt through both base fabrics to join them to one another. One or both woven base fabrics may be of the on-machine-seamable type.
In any event, the woven base fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce fabrics, and belts, to the dimensions required to fit particular positions in the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
In response to this need to produce fabrics in a variety of lengths and widths more quickly and efficiently, press fabrics have been produced in recent years using a spiral technique disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 5,360,656 shows a press fabric comprising a base fabric having one or more layers of staple fiber material needled thereinto. The base fabric comprises at least one layer composed of a spirally wound strip of woven fabric having a width which is smaller than the width of the base fabric. The base fabric is endless in the longitudinal, or machine, direction. Lengthwise threads of the spirally wound strip make an angle with the longitudinal direction of the press fabric. The strip of woven fabric may be flat-woven on a loom which is narrower than those typically used in the production of paper machine clothing.
The base fabric comprises a plurality of spirally wound and joined turns of the relatively narrow woven fabric strip. The fabric strip is woven from lengthwise (warp) and crosswise (filling) yarns. Adjacent turns of the spirally wound fabric strip may be abutted against one another, and the helically continuous seam so produced may be closed by sewing, stitching, melting or welding. Alternatively, adjacent longitudinal end portions of adjoining spiral turns may be arranged overlappingly, so long as the ends have a reduced thickness, so as not to give rise to an increased thickness in the area of the overlap. Further, the spacing between lengthwise yarns may be increased at the ends of the strip, so that, when adjoining spiral turns are arranged overlappingly, there may be an unchanged spacing between lengthwise threads in the area of the overlap.
In the case of dryer fabrics, in particular, such fabrics were produced by flat weaving and then joined together. Dryer fabrics that are used today are long and require a seam for installation, since dryer section frames are solid without cantilever components and thus prevent the use of endless woven fabrics. Accordingly, the fabrics must be installed with a seam, since they cannot be put on endless.
It should be noted that contemporary fabrics also include fabrics with non-woven bases. An example of a non-woven fabric is shown in U.S. Pat. No. 4,427,734, which discloses a wet press felt for use on papermaking machines. The wet press felt includes a conventional felt fabric and a multiple of non-woven layers of synthetic textile fibers needled to the felt. Interposed between the layers of synthetic textile fiber are mesh fabrics which support the individual non-woven layers and retard compaction of the overall construction. Such non-woven fabrics may be provided with seams like those of the woven fabrics in order to realize an “endless” non-woven fabric.
In addition to the aforenoted modified endless weaving which provides a seamable fabric, there exists other types of seams heretofore utilized, particularly in the case of dryer fabrics. For example, some flat woven dryer fabrics had clipper hook seams as are used in corrugator belts today. However, clipper hooks tend to corrode. More importantly, clipper hooks wear, do not flex well (they tend to bump around fabric support rolls), and the seam tends to mark the paper sheet.
Some fabrics and belts are seamed on a diagonal in a manner as set forth in U.S. Pat. No. 5,217,415 which has been found satisfactory for certain applications.
Seams can also be sewn on which involves a webbing sewn onto both cross-machine direction (“CD”) ends of the dryer fabric. The webbing contains loops which are meshed together to form the seam. The webbing, since it is out of plane and thicker than the fabric body, also tends to bump around fabric support rolls, marks the sheet, and has zero permeability, which further exacerbates the sheet marking problem. Since it is sewn on, the stitching is between the web and the fabric body. Once the stitching fails, the web will pull off, resulting in a “seam failure”.
The market today is dominated by fabrics having pin seams, with or without a spiral insert. These seams require MD yarns to be woven back into the structure body by hand or machine assisted. CD yarns must be raveled out. Yarn materials, counts and sizes, weaves dictate the seam properties and the seam properties (uniformity, strength) dictate yarn counts within a certain weave. These seams are expensive to make, since they are labor intensive. The strength and seam durability are dictated by material properties too, especially loop strength. “Brittle” materials which have poor loop strength but may have other good properties are not dryer fabric candidates because of this. To compensate for low seam loop strength one may have to compromise on the fabric structure itself. An example of a seam having a spiral insert can be found in U.S. Pat. No. 5,915,422.
Early metal forming fabrics which were flat woven and shipped open ended, were installed on the machine with the metal wire ends joined together by brazing or fusing the yarns by heat. This “butt seam” had some slight end overlap and the seam only lasted for a short period of time. There was no sewing, stitching, or adding in a synthetic spiral.
Another example of a butt seam can be found in the aforementioned U.S. Pat. No. 5,360,656. This seam is between adjacent strips of fabric and includes stitching. The seams, however, are not load bearing and are merely there to hold the strips together so that the “base” structures formed by these joined together strips can be handled through the manufacturing process.
U.S. Pat. Nos. 4,887,648 and 4,865,083 disclose various embodiments of pin seams in a four layer integrally woven fabric, both with and without spiral inserts. These patents disclose the use of loops formed from the MD yarns on each side of the dryer fabric. Thus, as noted above, the formation of these loops is a time intensive procedure. In order to avoid such a procedure, a spiral insert may be employed, such as that shown in FIG. 11 of these patents. Rather than meshing the loops from each edge together, a spiral insert meshes with the MD yarn formed loops. Thereafter, two pintles are inserted, one fixing each end of the dryer layer to the spiral insert to form the appropriate desired seam.
Obviously, there are other ways to provide seamable fabrics for use in papermaking and other industrial applications, with the foregoing being set forth merely as examples. However, as with anything, there is always a desire to improve on or provide an alternative to what has been done previously. Seamable fabrics are no exception. In this regard, heretofore providing a seam on a fabric has been relatively time consuming and labor intensive. If these are aspects that can be improved upon, this would obviously be a desirable result.
The present invention provides yet another approach toward forming the spirally continuous seam in a fabric of this type.